Device and method for purification of exhaust gases from an internal combustion engine

ABSTRACT

The invention relates to device for emission control of an internal combustion engine ( 10 ) including an exhaust tract ( 12 ) comprising a NO x  catalyst ( 14 ), and a reductant feeder ( 16 ) designed to deliver reductant to the exhaust tract ( 12 ) upstream of the NO x  catalyst ( 14 ). In accordance with the invention, the reductant feeder ( 16 ) comprises a reformer ( 18 ) designed to react gas exhausted by the engine ( 10 ) and fuel into a reformate serving as reductant. 
     In addition, the invention relates to a method for emission control of an internal combustion engine ( 10 ) wherein a NO x  catalyst ( 14 ) provided in the exhaust tract ( 12 ) is supplied with reductant. In this arrangement use is made of reformate generated by a reformer ( 18 ) as the reductant, the reformer ( 18 ) generating the reformate from the engine ( 10 ) exhaust gas and fuel.

The invention relates to a device for emission control of an internal combustion engine including an exhaust tract comprising a NO_(x) catalyst, and a reductant feeder designed to deliver reductant to the exhaust tract upstream of the NO_(x) catalyst. In addition the invention relates to a method for emission control of an internal combustion engine wherein a NO_(x) catalyst provided in the exhaust tract is supplied with reductant.

One problem associated with modern motor vehicles is the emission of nitrous oxides (NO_(x)) materializing in the combustion of gasoline or diesel in the engine, particularly at high combustion chamber temperatures. To reduce NO_(x) emissions catalyst systems are known for storing the NO_(x) and reducing it to safe nitrogen. From the generic DE 102 33 66 5 A1 it is already known for this purpose to inject reductant in the form of fuel into the exhaust tract upstream of the NO_(x) catalyst. Instead of injecting pure fuel as is known from DE 102 33 66 5 A1 use may be made of a reformate as the reductant. No matter what kind of reductant is selected, it needs to be introduced into the exhaust tract in counteracting the fluctuating back pressure of the exhaust system. For this purpose prior art makes use of high-performance blowers, air compressors or injectors, all of which add to the costs and the nuisance of frequent servicing.

The object of the present invention involves sophisticating generic devices and methods such that costly means requiring frequent servicing for introducing the reductant in the exhaust tract counteracting the fluctuating back pressure of the exhaust system are now eliminated.

This object is achieved by the features of the independent claims.

Advantageous aspects and further embodiments of the invention read from the dependent claims.

The device in accordance with the invention is a sophistication over generic prior art in that the reductant feeder comprises a reformer designed to react the gas exhausted by the engine and fuel into a reformate serving as the reductant. It is particularly with diesel engines that the exhaust gas of the engine contains an appreciable proportion of oxygen which in addition to the fuel is feedstock for generating a reformate. When branching off this exhaust gas immediately downstream of the engine it has a corresponding high pressure level. Due to this high pressure level of the branched-off exhaust gas it is possible in accordance with the invention to introduce the reformate upstream of the NO_(x) catalyst into the exhaust tract in thus eliminating costly means requiring frequent servicing needed as in prior art to generate the pressure required to introduce the reformate. The branched-off exhaust gas and fuel are mixed in the reformer and supplied to a reformer catalyst. In the subsequent reaction in the form of an exothermic partial oxidation a reformate gas having a proportion of the reducing gases hydrogen and carbon monoxide is generated. These gases are suitable for reducing the nitrous oxides in the NO_(x) catalyst to safe nitrogen.

For the device in accordance with the invention it is considered to be particularly advantageous when it is provided for that the exhaust gas supplied to the reformer is obtained via a exhaust tract branch-off disposed directly downstream of the engine. Directly down-stream of the engine the exhaust gas pressure is high and thus well suited to introduce the reformate in counteracting the back pressure in the exhaust tract.

In accordance with a preferred further embodiment of the device in accordance with the invention it is provided for that the exhaust gas supplied to the reformer is obtained via a exhaust tract branch-off comprising an exhaust gas metering device. This exhaust gas metering device permits introducing the amount of exhaust gas as needed in each case to generate the reformate to be supplied to the reformer. The exhaust gas metering device may work with open or closed loop control.

In conjunction with the arrangement as described above the exhaust gas metering device may comprise a valving apparatus. This valving apparatus may be, for example, a metering valve similar to a valve for returning the exhaust gas.

In addition or as an alternative thereto, it may be provided for in the device in accordance with the invention that the exhaust gas metering device comprises a blower which because of the high pressure level of the exhaust gas supplied to the blower can be designed with a much lower power level than needed in prior art.

The device in accordance with the invention can be sophisticated to advantage in that the exhaust gas supplied to the reformer is obtained via a exhaust tract branch-off disposed upstream of a further catalyst disposed upstream of the NO_(x) catalyst. This further catalyst may be, for example, the main catalyst of the emission control system, the exhaust gas being obtained upstream of the further catalyst and introduced into the NO_(x) catalyst in the exhaust tract.

At least in some aspects of the device in accordance with the invention it may be provided for that it comprises a fuel pump, designed to pump fuel from a fuel tank. The fuel pump may be in particular a fuel metering pump for pumping the fuel from the fuel tank in the amount as needed to generate the reformate in each case. This fuel pump may also feature open or closed loop control.

In accordance with yet another advantageous further embodiment of the device in accordance with the invention it is provided for that the fuel is obtained from a fuel line of the fuel system of the engine and that the fuel is supplied to the reformer via a fuel valving apparatus, the fuel line concerned may be, in particular, a pressurized fuel line, for example a common rail return. The fuel valving apparatus may be, in particular, a fuel metering valve which passes the amount of fuel as needed in each case to generate the reformate. This fuel valving apparatus may also feature open or closed loop control.

The method in accordance with the invention is a sophistication over prior art in that use is made of reformate generated by a reformer as the reductant, the reformer generating the reformate from engine exhaust gas and fuel. This achievement has the same advantages and features as recited for the device in accordance with the invention and thus to avoid tedious repetition reference is made to the comments in conjunction with the device in accordance with the invention.

The same applies in accordance with the following preferred aspects of the method in accordance with the invention, here too, reference being made to the comments in conjunction with the device in accordance with the invention.

In preferred aspects of the method in accordance with the invention it is provided for that the exhaust gas supplied to the reformer is obtained via a exhaust tract branch-off disposed directly downstream of the engine.

It is likewise considered to be an advantage of the method in accordance with the invention that the exhaust gas supplied to the reformer is obtained via a exhaust tract branch-off containing an exhaust gas metering device.

In this arrangement it is considered to be an advantage that the exhaust gas metering device comprises a valving apparatus.

In addition to or as an alternative thereto it may be provided for that the exhaust gas metering device comprises a blower.

In certain aspects of the method in accordance with the invention it may be provided for that the exhaust gas supplied to the reformer is obtained via a exhaust tract branch-off disposed at the input to a further catalyst disposed upstream of the NO_(x) catalyst.

In the method in accordance with the invention too, aspects come into consideration in which it is provided for that a fuel pump is included, designed to pump fuel from a fuel tank.

In this case it may be provided for in addition or as an alternative thereto that the fuel is obtained from a fuel line of the fuel system of the engine and that the fuel is supplied to the reformer via a fuel valving apparatus.

Of particularly advantage in the achievement in accordance with the invention is that it is independent of the exhaust back pressure of the exhaust system and thus of the load on the engine, because the reformer pressure is now always adapted to the level of the exhaust gas pressure. In other words, via the reformer system the system pressure is now always practically constant and independent of the load of the engine and exhaust back pressure.

Preferred embodiments of the invention will now be explained by way of example with reference to the corresponding drawings in which

FIG. 1 is a diagrammatic block diagram illustrating a first embodiment of the device in accordance with the invention suitable for implementing the method in accordance with the invention; and

FIG. 2 is a diagrammatic block diagram illustrating a second embodiment of the device in accordance with the invention likewise suitable for implementing the method in accordance with the invention.

Like components are identified in the drawings by like reference numerals as explained only once to avoid tedious repetition.

Referring now to FIG. 1, there is illustrated how an internal combustion engine 10 is assigned an exhaust tract 12 comprising a NO_(x) catalyst 14 and a further catalyst 24, the further catalyst 24 being the main catalyst. Disposed directly downstream of the engine 10 is a exhaust tract branch-off 20 connecting a reformer 18 via an exhaust gas metering device 22. In the embodiment as shown in FIG. 1 the exhaust gas metering device 22 is formed by a exhaust gas metering valve. A fuel pump 26 is provided to supply the reformer 18 with fuel metered from a fuel tank 28. The exhaust tract branch-off 20, the exhaust gas metering device 22, fuel pump 26 and reformer 18 all form together a reductant feeder. In the reformer 18 the branched-off exhaust gas and the fed fuel are mixed and supplied to a reformate catalyst (not shown) which is a component of the reformer 18. In the subsequent reaction a gaseous reformate is generated containing a proportion of the reducing gases hydrogen and carbon monoxide. The reformate as generated this way is introduced into the exhaust tract 12 upstream of the NO_(x) catalyst 14. Because the reformer pressure is always adapted to the actual exhaust gas pressure no special means are needed to overcome the exhaust back pressure on introducing the reformate into the exhaust tract 12. Via the reformer 18 the system pressure is now by the achievement in accordance with the invention practically constant and independent of the engine load and exhaust back pressure. Both the exhaust gas metering device 22 in the form of a metering valve as well as the fuel pump 26 can be operated with open or closed loop control. For this purpose a controller (not shown) may be provided which is also capable of providing open or closed loop control of the other components of the reformer 18.

Referring now to FIG. 2, there is illustrated a diagrammatic block diagram of a second embodiment of the device in accordance with the invention, likewise suitable for implementing the method in accordance with the invention. The embodiment as shown in FIG. 2 differs from the embodiment as shown in FIG. 1 in that the exhaust gas metering device 22 is formed by a blower and that instead of a fuel pump a fuel valving apparatus 32 is provided. The blower forming the exhaust gas metering device 22 may be a relatively low power blower since the exhaust tract branch-off 20 is subjected to a high exhaust gas pressure. The fuel valving apparatus 32 is achieved by a fuel metering valve disposed between the fuel line 30 of the fuel system of the engine 10 and the reformer 18. The fuel line 30 of the fuel system of the engine 10 may be, in particular, a fuel pressure line, for example a common rail return. This achievement is based on having discovered that there is no need for a separate fuel pump when a sufficiently high fuel pressure is available anyway.

In the embodiment as shown in FIG. 2 too, a controller (not shown) may be provided for activating the corresponding components as already explained in conjunction with the comments as to FIG. 1. The advantage of operation independent of the exhaust back pressure and engine load thus applies likewise to the embodiment as shown in FIG. 2.

It will be appreciated, of course, that the exhaust gas metering device may also be formed in the embodiment as shown in FIG. 2 too, by a valving apparatus; in the embodiment as shown in FIG. 1 a blower can be put to use as an alternative.

It is understood that the features of the invention as disclosed in the above description, in the drawings and as claimed may be essential to achieving the invention both by themselves or in any combination.

LIST OF REFERENCE NUMERALS

-   10 engine -   13 exhaust tract -   14 NO_(x) catalyst -   16 reductant feeder -   18 reformer -   20 exhaust tract branch-off -   22 exhaust gas metering device -   24 further catalyst -   26 fuel pump -   28 fuel tank -   30 fuel system line -   32 fuel valving apparatus 

1-16. (canceled)
 17. A device for emission control of an internal combustion engine including an exhaust tract comprising a NO_(x) catalyst, and a reductant feeder configured to deliver reductant to the exhaust tract upstream of the NO_(x) catalyst, wherein the reductant feeder comprises a reformer configured to react gas exhausted by the engine and fuel into a reformate serving as reductant.
 18. The device as set forth in claim 1, wherein the exhaust gas supplied to the reformer is obtained via a exhaust tract branch-off disposed directly downstream of the engine.
 19. The device as set forth in claim 1, wherein the exhaust gas supplied to the reformer is obtained via a exhaust tract branch-off comprising an exhaust gas metering device.
 20. The device as set forth in claim 19, wherein the exhaust gas metering device comprises a valving apparatus.
 21. The device as set forth in claim 19, wherein the exhaust gas metering device comprises a blower.
 22. The device as set forth in claim 17, wherein the exhaust gas supplied to the reformer is obtained via a exhaust tract branch-off disposed upstream of a further catalyst disposed upstream of the NO_(x) catalyst.
 23. The device as set forth in claim 17, further comprising a fuel pump, designed to pump fuel from a fuel tank.
 24. The device as set forth in claim 17, wherein the fuel is obtained from a fuel line of the fuel system of the engine and that the fuel is supplied to the reformer via a fuel valving apparatus.
 25. A method for emission control of an internal combustion engine wherein a NO_(x) catalyst provided in the exhaust tract is supplied with reductant, comprising: generating reformate from the engine exhaust gas and fuel using a reformer; and using the reformate generated by the reformer as reductant.
 26. The method as set forth in claim 25, wherein the exhaust gas supplied to the reformer is obtained via an exhaust tract branch-off disposed directly downstream of the engine.
 27. The method as set forth in claim 26, wherein the exhaust gas supplied to the reformer is obtained via an exhaust tract branch-off containing an exhaust gas metering device.
 28. The method as set forth in claim 27, wherein the exhaust gas metering device comprises a valving apparatus.
 29. The method as set forth in claim 27, wherein the exhaust gas metering device comprises a blower.
 30. The method as set forth in claim 25, wherein the exhaust gas supplied to the reformer is obtained via a exhaust tract branch-off disposed upstream of a further catalyst disposed upstream of the NO_(x) catalyst.
 31. The method as set forth in claim 25, wherein the fuel supplied to the reformer is delivered by a fuel pump.
 32. The method as set forth in claim 25, wherein the fuel is obtained from a fuel line of the fuel system of the engine and that the fuel is supplied to the reformer via a fuel valving apparatus. 